Neuronal distribution and functional characterization of the calcium channel α2δ‐2 subunit

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Abstract
The auxiliary calcium channel α2δ subunit comprises a family of three genes, α2δ‐1 to 3, which are expressed in a tissue‐specific manner. α2δ‐2 mRNA is found in the heart, skeletal muscle, brain, kidney, liver and pancreas. We report here for the first time the identification and functional characterization of α2δ‐2 splice variants and their mRNA distribution in the mouse brain. The splice variants differ in the α2 and δ protein by eight and three amino acid residues, respectively, and are differentially expressed in cardiac tissue and human medullary thyroid carcinoma (hMTC) cells. In situ hybridization of mouse brain sections revealed the highest expression of α2δ‐2 mRNA in the Purkinje cell layer of the cerebellum, habenulae and septal nuclei, and a lower expression in the cerebral cortex, olfactory bulb, thalamic and hypothalamic nuclei, as well as the inferior and superior colliculus. As the in situ data did not suggest a specific colocalization with any α1 subunit, coexpression studies of α2δ‐2 were carried out either with the high‐voltage‐gated calcium channels, α1C, α1E or α1A, or with the low‐voltage‐gated calcium channel, α1G. Coexpression of α2δ‐2 increased the current density, shifted the voltage dependence of channel activation and inactivation of α1C, α1E and α1A subunits in a hyperpolarizing direction, and accelerated the decay and shifted the steady‐state inactivation of the α1G current.